1. Technical Field
The present invention relates to a tissue insertion type ultrasonic probe, and in particular, to an ultrasonic probe used for inspection of a guide hole formed in a vertebral bone in spine surgery.
2. Background Art
An ultrasound diagnostic apparatus is an apparatus which forms an ultrasound image based on a reception signal obtained by transmission and reception of ultrasound to and from a tissue of a living body. The ultrasound diagnostic apparatus comprises a device body and an ultrasonic probe. The device body comprises a transmission unit, a reception unit, an image formation unit, a display, an operation panel, or the like, and the ultrasonic probe is detachably attached on the device body. The ultrasonic probe generally comprises an array transducer. The array transducer comprises a plurality of transducer elements which are aligned, and an ultrasound beam is formed by the plurality of transducer elements. A beam scanning plane is formed by electronic scanning of the ultrasound beam. The device body forms a two-dimensional tomographic image (B mode image) corresponding to the beam scanning plane based on a reception signal which is output from the ultrasonic probe. As the ultrasound image, in addition to the two-dimensional tomographic image, there are also known a two-dimensional bloodstream image, a Doppler image, a three-dimensional image, or the like.
A surgery method of fixing a plurality of vertebral bones forming the spine using metal components is used more and more widely, and is illustrated in FIG. 1. The spine comprises a plurality of vertebral bones 10 and 12. An intervertebral disk 14 is present between the vertebral bones 10 and 12. Two bolts (or screws) 16 and 18 are mounted on each of the vertebral bones 10 and 12; that is, in the configuration shown in FIG. 1, a total of four bolts are mounted. Two bolts 16 and 18 arranged on the right side of each of the vertebral bones 10 and 12 are connected by a metal rod 20. Similarly, two bolts (not shown) arranged on the left side of each of the vertebral bones 10 and 12 are connected by another metal rad. With such a method, a positional relationship between the two vertebral bones 10 and 12 is fixed.
In the above-described fixing method, before the two bolts are mounted on each vertebral bone, two guide holes (pilot holes) are formed in each vertebral bone. FIG. 2 shows the vertebral bone 10. The vertebral bone 10 comprises a vertebral body or centrum 22 and a vertebral arch 24. A vertebral foramen (spinal canal) 26 through which a nerve passes is formed in the vertebral bone 10. Two guide holes 28 and 30 must be formed at appropriate positions and with appropriate angles. In particular, entrance or approaching of the guide holes 28 and 30 to the vertebral foramen 26 must be avoided. If the bolt is mounted in such an inappropriate guide hole, the nerve passing through the vertebral foramen 26 may be damaged. In consideration of such circumstances, the guide holes 28 and 30 are carefully formed using a surgery drill. However, in the process of forming the guide holes 28 and 30, it is not possible to see with human eyes the interior of the guide holes 28 and 30.
In view of this, in the related art, a metal tool dedicated for tactile inspection is repeatedly used in the formation process of the guide holes 28 and 30. The metal tool comprises a long-and-narrow wire-like shaft portion, and a slightly wide grip portion connected to the long-and-narrow shaft portion. A tactile tip (or feeler) having a small spherical shape is provided on a front end of the shaft portion. The shaft portion and the grip portion are integrated; that is, the metal tool is formed as a single metal member elongated along a straight line. The front end of the metal tool is inserted into the guide hole while the grip of the metal tool is held, and the inner wall surface of the guide hole is traced with the tactile tip. With such a process, the shape of the inner wall surface of the guide hole can be indirectly understood with the tactile sense. Specifically, the shape of the projections and depressions on the inner wall surface is transmitted to the grip portion as a movement (vibration) of the tactile tip. By feeling the vibration with a plurality of fingertips, a user can indirectly understand the shape of the projections and depressions of the inner wall surface.
However, in the above-described inspection method with tactile sense using the metal tool, the state of the guide hole is not necessarily evaluated sufficiently. With the tactile sense method, a minute crack cannot be identified, and the inside of the guide hole cannot be observed. Even if the inspection by the tactile sense itself does not have any problem, inspection of the state of the guide hole (or structure of the vertebral bone) with a method other than the tactile sense is desired, from the viewpoint of further improving safety. In consideration of the above, realization of a tissue insertion type ultrasonic probe which can execute both tactile inspection and ultrasound diagnosis is demanded. With such an ultrasonic probe, it is possible to execute the ultrasound diagnosis immediately after the tactile inspection, to execute the tactile inspection immediately after the ultrasound diagnosis, or to simultaneously execute the tactile inspection and the ultrasound diagnosis, without inserting or removing the insertion unit.
U.S. Pat. No. 6,579,244 discloses a system which executes ultrasound diagnosis by inserting a member, which transmits and receives ultrasound, into a pilot hole formed in a bone. However, this reference fails to disclose a probe which can execute both tactile inspection and ultrasound diagnosis. In addition, this reference fails to disclose a specific structure (array transducer, line, etc.) for forming a two-dimensional tomographic image.
In an ultrasonic probe which is inserted into a tissue in order to form a tomographic image of inside of a tissue, generally, an array transducer comprising a plurality of transducer elements is provided. More specifically, the array transducer is embedded in a front end portion of an insertion tube (or insertion unit). A plurality of signal lines are connected to the plurality of transducer elements of the array transducer. Because of this, for example, a few tens or a few hundreds of cables must be passed inside the insertion tube, or a thick multi-core cable member which is a collective body of the cables must be passed inside the insertion tube. Because each cable comprises a central conductor and an insulating layer covering the central conductor, the overall thickness of the plurality of cables inevitably becomes thick. Because of this, in the related art, it has been difficult to reduce the diameter of the insertion tube or to maintain a large number of transmission/reception channels using a narrow insertion tube.
The above-described problem also applies to the ultrasonic probe which is used in spine surgery. Specifically, the outer diameter of the insertion tube of the ultrasonic probe is limited to a size which allows insertion into the guide hole having a diameter of 3 mm-4 mm (for example, an outer diameter of 3.0 mm or less), and, thus, the inner diameter is significantly small. It is very difficult to pass a large number of independent cables into an inside space of the insertion tube which is very small. When the tissue insertion type ultrasonic probe which can execute both tactile inspection and ultrasound diagnosis is considered, the insertion tube also functions as a medium which transmits the vibration from the tactile tip. In this case, if a large number of cables are densely stored inside the insertion tube, problems may be caused, such as disturbance or attenuation of the vibration.